POSSIBLE THERAPEUTICS FOR NEUROENDOCRINE AND GASTROINTESTINAL TUMORS AND NEUROPSYCHIATRIC DISEASES MAY BE DEVELOPED FROM PEPTIDE ANTAGONISTS OF THE CENTRAL NERVOUSSYSTEM CHOLECYSTOKININ RECEPTOR. STRUCTURALLY MODIFIED CHOLECYSTOKININ OCTAPEPTIDE FRAGMENTS WILL BE TESTED FOR INTERACTION WITH CHOLECYSTOKININ RECEPTORS IN A NEUROENDOCRINE CELL LINE, HUMAN SMALL-CELL LUNG CARCINOMA. THESE COMPOUNDS, MORE CLOSELY RESEMBLING NATURALLY OCCURRINGNEUROPEPTIDES, SHOULD CROSS-REACT LESS WITH OTHER CENTRAL NERVOUS SYSTEM RECEPTORS, RESULTING IN FEWER UNDESIRABLE SIDE EFFECTS. POTENT COMPOUNDS IDENTIFIED IN THE CELL ASSAYWILL BE FURTHER EVALUATED IN PHARMACOLOGICAL PRECLINICAL STUDIES IN THE PHASE II RESEARCH.